1. Field of the Invention
This invention relates to insulating glass windows and the manufacture thereof.
2. Background Information
Insulating glass units for use in windows or doors commonly comprise two or more parallel glass panes that are separated from one another by spacers along their edges. Various multiple-pane configurations are known in the art. Certain of these configurations have employed sheets of plastic in parallel spaced relation to the glass panes. If a multiple pane glass unit is to be assembled with a plastic sheet held in spaced relationship between two glass panes, the unit may be manufactured by applying a marginal spacer along the edges of one glass pane, the spacer extending away from the plane of the pane, adhering a heat-shrinkable film to the spacer, and then heat-shrinking the film to draw the film taut and flat. The second pane, also provided with a marginal spacer, is then attached, the film becoming sandwiched between the opposed marginal spacers of the two panes. In another embodiment, the film may be grasped by small springs that are held by or form a part of spacers separating the two glass panes from one another. Generally unbreakable mirrors may be formed by adhering a marginal spacer about the periphery of a sheet of plywood or the like, then adhering a heat-shrinkable, silvered plastic film to the spacers, and then heat-shrinking the film so that it becomes taut and flat to provide a mirrored surface.
In each of the described embodiments employing heat-shrinkable plastic film, the film is stretched over spacers held at the edge of a stiff pane or board, and the plastic film is then heated directly, typically by hot air. For multiple-pane glass units in which the plastic film is to be employed as an internal sheet between but spaced from parallel glass panes, the manufacturing methods cited above have been found difficult and time consuming, and require piecemeal construction methods.
Lizardo et al in U.S. Pat. No. 4,335,166, issued Jun. 15, 1982, describe manufacturing multiple-pane insulating glass window units by supporting a flexible, heat-shrinkable plastic sheet between parallel, spaced glass panes which are spaced from one another and from the plastic sheet (film) by means of spacers arranged about the edges of the glass panes. The panes are sealed to one another along their edges by the spacers and by a sealant adhered to edges of the plastic sheet to provide, with the heat-shrinkable plastic sheet, a sealed integral unit. The unit itself is then heated for a sufficient time and at a sufficient temperature to cause the plastic sheet to shrink and to become taut and wrinkle-free. The resulting integral unit upon cooling, requires no further manufacturing steps, and can be directly inserted into an appropriate frame for use as an insulating glass unit.
Further evaluation of the method claimed by Lizardo et al, found that successful construction depended upon the sealant materials used. For example, the edge sealant proposed by Lizardo et al, the two-part, room-temperature-curing resin identified as GE3:204 (manufactured by General Electric Company) may provide the necessary adhesion to hold the glass panes together along with the spacers, but experience finds that the plastic sheet became wrinkled in a short time after a multiple-pane insulating glass unit containing a plastic sheet was made. Although, in addition to GE3204, various silicone sealants may have been tried as edge sealant in making window units with an intermediate plastic sheet, as far as the present inventors know, to no silicone sealant has been satisfactory. Hood et al in U.S. Pat. No. 4,613,530, issued Sep. 23, 1986, teach that the edge sealant should be polyurethane. Although polyurethanes are useful as edge sealants for the kinds of multiple-pane insulating glass units described by Lizardo et al, they can be degraded by exposure to UV radiation if installed without a proper glazing cap to protect the sealant. Woodard et al in U.S. Pat. No. 5,308,662, issued May 3, 1994, describe the pros and cons of the various kinds of edge sealants and propose a mechanical means to overcome the degradation effects of UV radiation. Woodard et al teach that silicone sealants are resistant to light induced cross-linking and hardening which can cause serious failings in other kinds of sealants but are very permeable to water vapor. The organic sealants such as the polyurethanes and polysulfides are damaged by sunlight and thus Woodard et al have invented a construction for using a nonreflective dark tape positioned exactly right to overcome the impact of UV radiation on the edge sealant.
Hood et al in U.S. Pat. No. 5,156,894, issued Oct. 20, 1992, teach that suitable edge sealants for multiple-pane insulating glass units are curable, high modulus, low-creep, low-moisture-vapor-transmitting sealant, such as a polyurethane adhesive, for example the two-component polyurethanes marketed by Bostik, such as Bostik 3180-HM or 3190-HM. Vincent et al in U.S. Pat. No. 4,853,264, issued Aug. 1, 1989, teach that the same kind of edge sealants as Hood et al for use on curved triple-pane glazing in which a plastic sheet is intermediate between two glass panes. Vincent et al teach that the plastic sheet is anchored along the parallel curved edges but is not attached to the other edges and that the plastic sheet heat shrinks in the direction it is anchored.